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Some factors envolved in natural weaning processes in sheep
Applied Animal Ethology, 5 (1979) 43-59 o Elsevier Scientific Publishing Company, Amsterdam - Printed in The Netherlands
SOME FACTORS INVOLVED SHEEP
G.W. ARNOLD’,
IN NATURAL
43
WEANING PROCESSES IN
S.R. WALLACE’ and R.A. MALLER’
’Division of Land Resources Management,
CSIRO, Private Bag, P.O., Wembley, W.A. 6014 (Australia) 2Division of Mathematics and Statistics, CSIRO, Private Bag, P.O., Wembley, W.A. 6014 (Australia) (Received 18 October 1977)
ABSTRACT Arnold, G.W., Wallace, S.R. and Maller, R.A., 1979. Some factors involved in natura1 weaning processes in sheep. Appl. Anim. Ethol., 5: 43-50. Two studies were done to define the factors influencing the time of natura1 weaning in sheep. The milk production of ewes was measured during four-hour periods each week at varying stages of lactation. Lambs were separated from the ewes during this period before being reunited and the behavioural responses of each to the other were recorded. The responses were classed according to an arbitrary system defined to gauge the current strength of ewe-lamb attachments. In the first study, measurements were made on Merino and Dorset Horn sheep. Whilst milk yield declined continuously during lactation, the nature of ewe-lamb bonds did not. They remained constant up to about 100 days after birth. Thereafter, the attachments weakened rapidly, with some differences between the two breeds. In the second study, Merino ewes on a high plane of nutrition had a higher milk yield throughout lactation than ewes on a low plane of nutrition. The ewe-lamb bond remained unchanged for 130 days in the high plane group but changed substantially in the low plane group. It is concluded that milk yield in the ewe is a major determinant of the strength of the ewe-lamb bond, with a threshold leve1 below which weaning occurs.
INTRODUCTION
Among domestic sheep, there are gradual changes in the strength of ewelamb bond from birth. Initially, the bond is established by the ability of the ewe to recognise the lamb since the lamb is unable to discriminate the ewe until it is about 6 days old (Arnold et al., 1975). After this age, the maintenance of the bond appears to become increasingly dependent on the lamb (McBride et al., 1967) as the ewe and lamb behave more and more independent ly (Morgan and Arnold, 1974). The lamb wil1 continue to maintain contact with the ewe when grazing, and especially when resting, up to 190 days of
44
age (Arnold and Pahl, 1974) even if it is not obtaining milk from the ewe. The lamb is weaned, in our terminology, when the ewe actively prevents the lamb from sucking. Collias (1956) states that the greatest age at which a lamb has been seen to be nursed is 135 days. In Bighorn sheep (Ouis canadensis), Geist (1969) found that lambs were generally not suckled after 180 days of age. However, in another locality Spencer (1943) reported that nursing continued periodically for much longer. Under most husbandry conditions lambs are physically separated from their dams. This may occur whilst the lamb is stil1obtaining milk from its dam or it may have been naturally weaned by the time it is separated. In both situations the main social bond the young animal has had is broken. The separate effects, on lamb behaviour and performance, of loss of milk supply and of breaking the social bond have not been studied, nor is much known about the process of natural weaning. The changes in maternal care which lead to weaning may be related to physiological changes in the ewe, particularly with decline in lactation, or they may simply be due to changes in the behaviour of the lamb with increasing age. This paper reports on studies in which changes with age in the ewe-lamb bond were examined in relation to the lactational state of the ewes. MATERIALS
AND METHODS
Merino and Dorset Horn sheep have been maintained for 12 years as natural flocks (i.e. where age and sex classes had not been separated) at the CSIRO Yalanbee Experiment Station, Bakers Hill, Western Australia. Thirty Merino ewes (average age 4.5 years) having had from 0 to 8 previous parturitions and 22 Dorset Horn ewes (average age 3 years) having had from 0 to 6 previous parturitions, were studied. Some ewes had already lambed in March and so were studied from then onwards. Others that lambed late in the period were studied for only the first few weeks after lambing. Thus, there were unequal numbers of ewes of each breed for different time periods after lambing. In a second study, 2 groups of 25 Merino ewes were fed ad libitum in yards (as described by Arnold et al., 1977) on rations containing either 8 or 16% crude protein until an average of 134 days after parturition. Milk yields were estimated using the oxytocin technique (McCance, 1959) with either hand (Study 1) or machine (Study 2) milking once each week over a 4-hour period. Milking was stopped when the 24 h milk yield was
45
age classes for milk yield varied from 2 to 18. The number of observations in each class of behaviour is given for the first study in Table 11; no data were available on Dorset Horns until the sixth week after lambing. In the second study in farm-yards, milking was stopped after 120 days and behavioural observation after 140 days. TABLE 1 Classes of behaviour responses Class
Behaviour 1. Both ewe and lamb cail, lamb finds ewe and sucks
A
2. Either ewe or lamb cail, lamb finds ewe and sucks
A
3. Both ewe and lamb cail, lamb finds ewe but is not ailowed to suck
B
4. Either ewe or lamb cail, lamb finds ewe but is not ailowed to suck
B
W eaned
5. Both ewe and lamb cail, they join up and waik away with no attempt to suck 6. Either ewe or lamb cails, join up and waIk away with no attempt to suck 7. Ewe and lamb join up, no cailing and no attempt to suck 8. NO visible interest shown by ewe or lamb TABLE 11 Distribution of classes of behaviour by ages (proportions Age in days Merinos 0-50 50-70 70-90 90-110 110-150 150-200 200-250 250-300
A
106 55 49 47 19 0 0 0
Dorset Horns 0-50 66 50-70 45 70-90 37 90-110 33 110-150 27 150-200 5 200-250 0 250-300 0
(1.0) (0.96) (0.88) (0.75) (0.17)
(1.00) (1.00) (0.84) (0.65) (0.29) (0.09)
B
C
0 1 3 6 11 4 0 0
0 1 4 10 74 21 0 0
0 0 2 5 10 1 0 0
(0.05) (0.10) (0.10) (0.08)
D
(0.07) (0.15) (0.68) (0.44)
0 1 0 0 4 0 6 0
(0.02) (0.16) (0.47) (0.52)
0 0 2 5 10 26 10 0
0 0
(0.05) (0.10) (0.11) (0.02)
3 8 44 29 0 0
in parentheses) E
0 0 0 0
(0.04) 23 16 4
(0.05) (0.09) (0.11) (0.02)
(0.48) (1.00) (1.00)
0 0 0 0
3 20 16 3
(0.02) (0.35) (1.00) (1.00)
46
RESULTS
Changes in behavioural responses with time after parturition and in milk yield are shown for the two studies in Figs.1 and 2. In the first study, some Merino ewes began to prevent their lambs sucking at an earlier age than did Dorset Horn ewes but in both flocks there was a rapid decrease in the percentage of lambs allowed to suck between 75 and 125 days after parturition. Al1 Merino ewes had weaned their lambs by 135 days but some Dorset Horn ewes were stil1suckling their lambs up to 160 days of age. A xz test of the differente between breeds in the proportion of Class A bonds in different age classes was not significant.
Fig.1. Changes in the percentage of ewes sllowing lambs to suck and in milk yield with time since parturition - Study 1. Note: the lines are hand fitted.
.
HIGH
PROTEIN
D LOW PROTEIN
I
0
60 DAYS SINCE
i
I
100
150
PARTURITION
Fig. 2. Changes in the percentage of ewes allowing lambs to suck and in milk yield with time since parturition - Study 2. Note: the lines are hand fitted.
The data on milk production were log-transformed to linearise them and achieve homogeneity. Means over sheep were obtained for each breed for each age class. A regression (weighted for the different numbers of observations at each age, which varied from 2 to 18) of mean log milk production on lamb age was fitted for each breed; the data were best represented by straight lines with different slopes (P < 0.05) and different intercepts (P < 0.001). The back transformed regressions were: Merino: Milk yield (cc/day) = 1353 exp(-0.0106 days) Dorset Horn: Milk yield (cc/day) = 1537 exp(-0.0064 days) The first regression account& for 87% of the variante between days, and the second, 45%; that the latter was the poorer fit was due to a comparatively high milk yield by some Dorset Horn ewes at older lamb ages. The data clearly show that Dorset Hom ewes had a higher milk yield throughout lactation. The time when behavioural responses first changed appeared to be once milk yield had declined to
49
study. There was also some indication of a “threshold” leve1 of milk supply, below which rejection of sucking occurs. The average (“threshold”) value for these two groups of Merinos was 550 cc day-‘. Further work is needed on this point. From a husbandry viewpoint, the nutritional impact of separating lambs from their dams wil1 depend on the leve1 of milk yield in the ewes. The better they are fed the longer the lambs wil1 get milk from the ewe because the ewes wil1 delay natural weaning. A!though 0-- the ---- lambs were not observed in the field to find out when nursing ceased, it seems reasonable to assume that it was at a similar age to the persistent occurrence of Class B behaviour. In both studies it was found that rejection of sucking by the ewe was almost always completed within a week, i.e. if lambs were rejected for one week in the tests, most were rejected in subsequent weeks. Thus, weaning is quite sudden, although the lambs wil1 have been getting progressively less milk, and the husbandry practice of sudden separation of the ewe and lamb differs mainly in the breaking of the ewelamb bond. This requires that the lambs develop a completely new social organization without any comfort from sucking. However, whether it is sufficiently disturbing to affect feeding behaviour, and thus lamb performance, :_ IS._-1_._--.UIlKIlUWII. The observations in the first study indicate that most lambs were weaned by day 150. The lambs, however, quite often attempted to suck weeks after they had been weaned. After 200 days no lamb ever tried to suck. Thus weaning in both Merinos and Dorset Horn sheep appears to be completed at a similar age to that reported previously for Bighorn sheep by Geist (1969). The lack of mutual interest by most of the mothers and offspring after 200 days in the natural flocks agrees with the observations of Arnold and Pahl(1974) that after 5 months of age lambs of 4 breeds showed decreasing interest in the behaviour of their dams. However, in husbanded flocks such as those studied by Hunter and Milner (1963) in which ewe lambs are not separated from tlne ewes, the lambs usually remain in the same home range as their dams. Whether this occurs in Merino and Dorset Horn sheep is currently being studied. ACKNOWLEDGEMENTS
The authors are grateful for skilled assistance in the measurements by Messrs. 1. Cook, D.A. Huston and L.A. Osborne and to Mrs. A. Pennock for assistance with the analysis.
REFERENCES Arnold, G.W. and Pahl, P.J., 1974. Some aspects of social behaviour in sheep. Anim. Behav., 22: 594-600.
50
Arnold, G.W., Boundy, C.A.P., Morgan, P.D. and Bartle, G., 1975. The roles of sight and hearing in the lamb in the location and discrimination between ewes. Appl. Anim. Ethol., 1: 167-176. Arnold, G.W., Wallace, S.R. and de Boer, ES., 1977. The effect of lupin grain supplement on lamb birthweight and growth rate and on milk production of Merino ewes. Aust. J. Exp. Agric. Anim. Husb., 17: 915-919. Collias, N.E., 1956. The analysis of socialisation in sheep and goats. Ecology, 37: 228-239. Geist, V., 1969. Ovis canadensis (Bovidae) Sociology of young. Encyclopaedia Cinematographics, E1336/1968. Hunter, R.F. and Milner, C., 1963. The behaviour of individual related and groups of South country Cheviot hill sheep. Anim. Behav., 11: 507-513. McBride, G., Arnold, G.W., Alexander, G. and Lynch, J.J., 1967. Ecological aspects of the behaviour of domestic animals. Proc. Ecol. Sec. Aust., 2: 133-165. McCance, I., 1959. The determination of milk yield in the Merino ewe. Aust. J. Agric. Res., 10: 839-853. Morgan, P.D. and Arnold, G.W., 1974. Behavioural relationships between Merino ewes and lambs during the four weeks after birth. Anim. Prod., 19: 169-176. Spencer, C.C., 1943. Notes of the life history of Rocky Mountain Bighorn sheep in Tarryall Mountains of Colorado. J. Mammal., 24: 1-10.
SOME FACTORS INVOLVED SHEEP
G.W. ARNOLD’,
IN NATURAL
43
WEANING PROCESSES IN
S.R. WALLACE’ and R.A. MALLER’
’Division of Land Resources Management,
CSIRO, Private Bag, P.O., Wembley, W.A. 6014 (Australia) 2Division of Mathematics and Statistics, CSIRO, Private Bag, P.O., Wembley, W.A. 6014 (Australia) (Received 18 October 1977)
ABSTRACT Arnold, G.W., Wallace, S.R. and Maller, R.A., 1979. Some factors involved in natura1 weaning processes in sheep. Appl. Anim. Ethol., 5: 43-50. Two studies were done to define the factors influencing the time of natura1 weaning in sheep. The milk production of ewes was measured during four-hour periods each week at varying stages of lactation. Lambs were separated from the ewes during this period before being reunited and the behavioural responses of each to the other were recorded. The responses were classed according to an arbitrary system defined to gauge the current strength of ewe-lamb attachments. In the first study, measurements were made on Merino and Dorset Horn sheep. Whilst milk yield declined continuously during lactation, the nature of ewe-lamb bonds did not. They remained constant up to about 100 days after birth. Thereafter, the attachments weakened rapidly, with some differences between the two breeds. In the second study, Merino ewes on a high plane of nutrition had a higher milk yield throughout lactation than ewes on a low plane of nutrition. The ewe-lamb bond remained unchanged for 130 days in the high plane group but changed substantially in the low plane group. It is concluded that milk yield in the ewe is a major determinant of the strength of the ewe-lamb bond, with a threshold leve1 below which weaning occurs.
INTRODUCTION
Among domestic sheep, there are gradual changes in the strength of ewelamb bond from birth. Initially, the bond is established by the ability of the ewe to recognise the lamb since the lamb is unable to discriminate the ewe until it is about 6 days old (Arnold et al., 1975). After this age, the maintenance of the bond appears to become increasingly dependent on the lamb (McBride et al., 1967) as the ewe and lamb behave more and more independent ly (Morgan and Arnold, 1974). The lamb wil1 continue to maintain contact with the ewe when grazing, and especially when resting, up to 190 days of
44
age (Arnold and Pahl, 1974) even if it is not obtaining milk from the ewe. The lamb is weaned, in our terminology, when the ewe actively prevents the lamb from sucking. Collias (1956) states that the greatest age at which a lamb has been seen to be nursed is 135 days. In Bighorn sheep (Ouis canadensis), Geist (1969) found that lambs were generally not suckled after 180 days of age. However, in another locality Spencer (1943) reported that nursing continued periodically for much longer. Under most husbandry conditions lambs are physically separated from their dams. This may occur whilst the lamb is stil1obtaining milk from its dam or it may have been naturally weaned by the time it is separated. In both situations the main social bond the young animal has had is broken. The separate effects, on lamb behaviour and performance, of loss of milk supply and of breaking the social bond have not been studied, nor is much known about the process of natural weaning. The changes in maternal care which lead to weaning may be related to physiological changes in the ewe, particularly with decline in lactation, or they may simply be due to changes in the behaviour of the lamb with increasing age. This paper reports on studies in which changes with age in the ewe-lamb bond were examined in relation to the lactational state of the ewes. MATERIALS
AND METHODS
Merino and Dorset Horn sheep have been maintained for 12 years as natural flocks (i.e. where age and sex classes had not been separated) at the CSIRO Yalanbee Experiment Station, Bakers Hill, Western Australia. Thirty Merino ewes (average age 4.5 years) having had from 0 to 8 previous parturitions and 22 Dorset Horn ewes (average age 3 years) having had from 0 to 6 previous parturitions, were studied. Some ewes had already lambed in March and so were studied from then onwards. Others that lambed late in the period were studied for only the first few weeks after lambing. Thus, there were unequal numbers of ewes of each breed for different time periods after lambing. In a second study, 2 groups of 25 Merino ewes were fed ad libitum in yards (as described by Arnold et al., 1977) on rations containing either 8 or 16% crude protein until an average of 134 days after parturition. Milk yields were estimated using the oxytocin technique (McCance, 1959) with either hand (Study 1) or machine (Study 2) milking once each week over a 4-hour period. Milking was stopped when the 24 h milk yield was
45
age classes for milk yield varied from 2 to 18. The number of observations in each class of behaviour is given for the first study in Table 11; no data were available on Dorset Horns until the sixth week after lambing. In the second study in farm-yards, milking was stopped after 120 days and behavioural observation after 140 days. TABLE 1 Classes of behaviour responses Class
Behaviour 1. Both ewe and lamb cail, lamb finds ewe and sucks
A
2. Either ewe or lamb cail, lamb finds ewe and sucks
A
3. Both ewe and lamb cail, lamb finds ewe but is not ailowed to suck
B
4. Either ewe or lamb cail, lamb finds ewe but is not ailowed to suck
B
W eaned
5. Both ewe and lamb cail, they join up and waik away with no attempt to suck 6. Either ewe or lamb cails, join up and waIk away with no attempt to suck 7. Ewe and lamb join up, no cailing and no attempt to suck 8. NO visible interest shown by ewe or lamb TABLE 11 Distribution of classes of behaviour by ages (proportions Age in days Merinos 0-50 50-70 70-90 90-110 110-150 150-200 200-250 250-300
A
106 55 49 47 19 0 0 0
Dorset Horns 0-50 66 50-70 45 70-90 37 90-110 33 110-150 27 150-200 5 200-250 0 250-300 0
(1.0) (0.96) (0.88) (0.75) (0.17)
(1.00) (1.00) (0.84) (0.65) (0.29) (0.09)
B
C
0 1 3 6 11 4 0 0
0 1 4 10 74 21 0 0
0 0 2 5 10 1 0 0
(0.05) (0.10) (0.10) (0.08)
D
(0.07) (0.15) (0.68) (0.44)
0 1 0 0 4 0 6 0
(0.02) (0.16) (0.47) (0.52)
0 0 2 5 10 26 10 0
0 0
(0.05) (0.10) (0.11) (0.02)
3 8 44 29 0 0
in parentheses) E
0 0 0 0
(0.04) 23 16 4
(0.05) (0.09) (0.11) (0.02)
(0.48) (1.00) (1.00)
0 0 0 0
3 20 16 3
(0.02) (0.35) (1.00) (1.00)
46
RESULTS
Changes in behavioural responses with time after parturition and in milk yield are shown for the two studies in Figs.1 and 2. In the first study, some Merino ewes began to prevent their lambs sucking at an earlier age than did Dorset Horn ewes but in both flocks there was a rapid decrease in the percentage of lambs allowed to suck between 75 and 125 days after parturition. Al1 Merino ewes had weaned their lambs by 135 days but some Dorset Horn ewes were stil1suckling their lambs up to 160 days of age. A xz test of the differente between breeds in the proportion of Class A bonds in different age classes was not significant.
Fig.1. Changes in the percentage of ewes sllowing lambs to suck and in milk yield with time since parturition - Study 1. Note: the lines are hand fitted.
.
HIGH
PROTEIN
D LOW PROTEIN
I
0
60 DAYS SINCE
i
I
100
150
PARTURITION
Fig. 2. Changes in the percentage of ewes allowing lambs to suck and in milk yield with time since parturition - Study 2. Note: the lines are hand fitted.
The data on milk production were log-transformed to linearise them and achieve homogeneity. Means over sheep were obtained for each breed for each age class. A regression (weighted for the different numbers of observations at each age, which varied from 2 to 18) of mean log milk production on lamb age was fitted for each breed; the data were best represented by straight lines with different slopes (P < 0.05) and different intercepts (P < 0.001). The back transformed regressions were: Merino: Milk yield (cc/day) = 1353 exp(-0.0106 days) Dorset Horn: Milk yield (cc/day) = 1537 exp(-0.0064 days) The first regression account& for 87% of the variante between days, and the second, 45%; that the latter was the poorer fit was due to a comparatively high milk yield by some Dorset Horn ewes at older lamb ages. The data clearly show that Dorset Hom ewes had a higher milk yield throughout lactation. The time when behavioural responses first changed appeared to be once milk yield had declined to
49
study. There was also some indication of a “threshold” leve1 of milk supply, below which rejection of sucking occurs. The average (“threshold”) value for these two groups of Merinos was 550 cc day-‘. Further work is needed on this point. From a husbandry viewpoint, the nutritional impact of separating lambs from their dams wil1 depend on the leve1 of milk yield in the ewes. The better they are fed the longer the lambs wil1 get milk from the ewe because the ewes wil1 delay natural weaning. A!though 0-- the ---- lambs were not observed in the field to find out when nursing ceased, it seems reasonable to assume that it was at a similar age to the persistent occurrence of Class B behaviour. In both studies it was found that rejection of sucking by the ewe was almost always completed within a week, i.e. if lambs were rejected for one week in the tests, most were rejected in subsequent weeks. Thus, weaning is quite sudden, although the lambs wil1 have been getting progressively less milk, and the husbandry practice of sudden separation of the ewe and lamb differs mainly in the breaking of the ewelamb bond. This requires that the lambs develop a completely new social organization without any comfort from sucking. However, whether it is sufficiently disturbing to affect feeding behaviour, and thus lamb performance, :_ IS._-1_._--.UIlKIlUWII. The observations in the first study indicate that most lambs were weaned by day 150. The lambs, however, quite often attempted to suck weeks after they had been weaned. After 200 days no lamb ever tried to suck. Thus weaning in both Merinos and Dorset Horn sheep appears to be completed at a similar age to that reported previously for Bighorn sheep by Geist (1969). The lack of mutual interest by most of the mothers and offspring after 200 days in the natural flocks agrees with the observations of Arnold and Pahl(1974) that after 5 months of age lambs of 4 breeds showed decreasing interest in the behaviour of their dams. However, in husbanded flocks such as those studied by Hunter and Milner (1963) in which ewe lambs are not separated from tlne ewes, the lambs usually remain in the same home range as their dams. Whether this occurs in Merino and Dorset Horn sheep is currently being studied. ACKNOWLEDGEMENTS
The authors are grateful for skilled assistance in the measurements by Messrs. 1. Cook, D.A. Huston and L.A. Osborne and to Mrs. A. Pennock for assistance with the analysis.
REFERENCES Arnold, G.W. and Pahl, P.J., 1974. Some aspects of social behaviour in sheep. Anim. Behav., 22: 594-600.
50
Arnold, G.W., Boundy, C.A.P., Morgan, P.D. and Bartle, G., 1975. The roles of sight and hearing in the lamb in the location and discrimination between ewes. Appl. Anim. Ethol., 1: 167-176. Arnold, G.W., Wallace, S.R. and de Boer, ES., 1977. The effect of lupin grain supplement on lamb birthweight and growth rate and on milk production of Merino ewes. Aust. J. Exp. Agric. Anim. Husb., 17: 915-919. Collias, N.E., 1956. The analysis of socialisation in sheep and goats. Ecology, 37: 228-239. Geist, V., 1969. Ovis canadensis (Bovidae) Sociology of young. Encyclopaedia Cinematographics, E1336/1968. Hunter, R.F. and Milner, C., 1963. The behaviour of individual related and groups of South country Cheviot hill sheep. Anim. Behav., 11: 507-513. McBride, G., Arnold, G.W., Alexander, G. and Lynch, J.J., 1967. Ecological aspects of the behaviour of domestic animals. Proc. Ecol. Sec. Aust., 2: 133-165. McCance, I., 1959. The determination of milk yield in the Merino ewe. Aust. J. Agric. Res., 10: 839-853. Morgan, P.D. and Arnold, G.W., 1974. Behavioural relationships between Merino ewes and lambs during the four weeks after birth. Anim. Prod., 19: 169-176. Spencer, C.C., 1943. Notes of the life history of Rocky Mountain Bighorn sheep in Tarryall Mountains of Colorado. J. Mammal., 24: 1-10.